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    <script>
        var arr = [1,2,3];
        var res = arr.toString();
        console.log(typeof res);
        console.log(arr);
        //在js中每一个对象都拥有一个__proto__指向原型对象
        console.log(arr.__proto__);
        console.log(arr.__proto__==Array.prototype);//true
        console.log(arr.__proto__.__proto__==Object.prototype);//true
        console.log(arr.__proto__.__proto__.__proto__);//null
    </script>
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